1. Field of the Invention
This invention relates to a drive system for ventilator comprising a fan driven by an electric motor, and more particularly to a ventilator drive system provided with a humidity sensor for sensing the relative humidity in a room to be ventilated, thereby automatically starting a ventilating operation before the occurrence of the dewing on indoor side surfaces of walls of the room.
2. Description of the prior Art
Bathroom ventilation systems are well known in the art. One of such bathroom ventilation systems is disclosed in Japanese patent Laid-open Application No. 58-156134. In this bathroom ventilation system, a ventilating unit is provided in a bathroom and comprises a fan for exhausting an indoor air to the outdoors and introducing an outdoor air into the bathroom and an electric motor for driving the fan. A humidity sensor is also provided in the bathroom for sensing the relative humidity in the bathroom.
According to the above described bathroom ventilation system, the humidity sensor produces a signal when the relative humidity in the bathroom is increased to a reference value set therein or above. The operation of the ventilating unit is automatically started based on the signal produced by the humidity sensor, thereby exhausting a humid air from the bathroom. Bathroom walls or the like may thus be protected against the humid air.
Whereas, an average temperature reaches 20.degree. C. and the relative humidity only increases to 40% in a room such as a living room when the heating operation is performed. Although the relative humidity in the bathroom reaches 90%, it does not increase so much in the living room. Whereas, the temperature of the room walls is generally decreased in winter since the outdoor side surfaces of the room walls are brought into contact with cold outdoor air. When the temperature of the room walls is decreased to, for example, 9.degree. C. as the dew-point temperature or below, the dewing occurs on the indoor side surfaces of the room walls even if the indoor temperature reaches 20.degree. C. with the relative humidity of 40%, thereby damaging the room walls and the like.
In the above mentioned circumstances, even when the prior art ventilation system described above is applied to the living room or the like. The occurrence of the dewing cannot be prevented. The reason for this is that the operation of the ventilating unit is started when the relative humidity in the room reaches 90%. Whereas, the relative humidity in the living room cannot generally be increased to 90%. Should the relative humidity of the living room be increased to 90%, some measure would artificially be taken to decrease the relative humidity. Furthermore, the reason is that the occurrence of the dewing on the indoor side surface of the room wall is influenced by the outdoor temperature even when the relative humidity in the room takes a relatively small value such as 40%.